Pneumatic driving tool with a fail-safe mechanism

ABSTRACT

A pneumatic driving tool is provided which incorporates a failsafe mechanism for preventing damage to the tool when an abnormal operating condition occurs. The mechanism includes an elongated cylinder and a piston mounted within said cylinder for normal reciprocatory movement between longitudinally spaced first and second positions. If the piston moves to a third position which is adjacent the second position but at a greater distance from said first position, due to an abnormal wear condition, the piston will automatically remain at said third position until the abnormal wear condition is corrected.

Perkins [451 Main 2%, w72

[54] IPNEIUMAII@ DRIVING 'IOOL WITH A 2,463,537 3/1949 Haar er al 9i/416FAILSAFE MECHANISM 3,037,466 4/i963 "robios 9i/417 A [72] Inventor:Garry R. Perkins, Cary, lll. 1an-man, Examie, paul E, Maslousky [73]Assignee: Spotnails, Inc., Rolling Meadows, Ill. Anomeynpendleton NeumanWuams & Anderson [22] Filed: Nov. 24, 1969 [57] ABSTRACT [2l] APPL N01879,316 A pneumatic driving tool is provided which incorporates afail-safe mechanism for preventing damage to the tool when [52] U s Cl91/417 A 91/402 92/85 an abnormal operating condition occurs. Themechanism in- [51] In't 'Cl FlSb 15/22 F0 It; 1 U02 cludes an elongatedcylinder and a piston mounted within said [58] Fied 91/17 A 416 402 399461 cylinder for normal reciprocatory movement between longitudinallyspaced first and second positions. lf the piston moves to a thirdposition which is adjacent the second position but at [56] ReferencesCited a greater distance from said first position, due to an abnormalUNITED STATES PATENTS wear condition, the piston will automaticallyremain at said 3 O5] 135 8/1962 s h 91/417 A third position until theabnormal wear condition is corrected.

mit 3,147,670 8/1964 Spencer ..91/461 9 Claims, 14 Drawing Figures 3 T lzo 42 v I/w 255 PATENTEUMARea ma 3,551,740

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PATENTEUMARea i972 3,651,740

sum 3 uf 3 AWF /N Ve .uref @www12 Pemf/us Bf? P&N.DLETOU, Meu/AfmSemo/.D (VILL/m45 #Troma/6 VS lPNEUMATIC DRIVING TOOL WllTllil AFAIL-SAFE MECHANISM BACKGROUND OF THE INVENTION The basic modus operandiof pneumatic driving tools has remained the same for years, namely apressure-actuated linear one way motion imparts a driving blow against afastener or the like causing the same to be expelled from the tool anddriven into a predetermined work piece. The means for imparting such adriving blow is generally effected through a single or double spool typepiston having a driver blade or the like affixed to the leading orfastener-contacting end thereof. The piston is reciprocally mountedwithin a suitable cylinder. Upon completion of the driving or firingstroke, the leading end of the piston strikes a resilient bumper whichis positioned at the lower terminus of the cylinder. The bumper which isnormally formed of rubber or a rubberlike material, is adapted to absorbthe excess impacting force of the piston and cushion same. The return ofthe piston to its firing position may be accomplished by springs,trapped air, or the like.

In recent years the utility of pneumatic driving tools has expandedconsiderably with the result that in many instances the power capacitiesof the tools have been increased substantially. With the more powerfultools maintenance thereof has become more difficult and costly. Onesource of maintenance problems has been the rapid deterioration of thebumpers which are used in such tools. Unless frequent inspection andreplacement of said bumpers are made, serious damage can result, such asbreaking of the driver blade and/or the piston, scarring of the cylinderwall, or in extreme cases the housing for the cylinder becomes fracturedresulting in the whole tool being replaced. ln order to avoid suchproblems, many users replace the bumpers periodically whether theyrequire it or not. Such a practice, however, may become costly andresult in an inordinate amount of downtime for the tool.

SUMMARY OF THE INVENTION Thus, it is an object of this invention toprovide a pneumatic tool embodying a fail-safe mechanism which minimizesthe maintenance of said tool and yet, markedly extends the useful lifethereof.

lt is a further object of this invention to provide a pneumatic toolwherein early detection of bumper deterioration can be readily effectedwithout disassembly of the tool and thus prevent the occurrence ofserious damage to the tool.

It is a further object of this invention to provide a pneumatic toolembodying a fail-safe mechanism which is simple in construction and maybe readily incorporated in various types of pneumatic driving tools.

Further and additional objects will appear from the description,accompanying drawings, and appended claims.

ln accordance with one embodiment of this invention a pneumaticallyoperated device is provided which comprises an elongated cylinder, and adouble spool type piston disposed therein. The piston in normaloperation reciprocates within the cylinder between longitudinally spacedfirst and second positions. ln an abnormal operational situation,however, the piston is rendered immovable and is disposed at a thirdposition. Such an abnormal situation is frequently due to the wear orbreakdown of the resilient bumper which under normal conditions engagesthe moving piston and absorbs or dampens its kinetic energy when thepiston reaches its second position and prior to the piston returning toits rst position. The third position is disposed adjacent to the secondposition but at a greater distance from the rst position. The doublespool type piston is provided with a transversely extending, airpressure responsive head which is in sliding, sealing engagement withthe interior surface of the cylinder. ln addition to the head, thepiston includes a transversely extending air pressure responsive,annular flange which is longitudinally spaced from the head. The annularflange is adapted to be in sealing engagement with the cylinder interiorsurface only when the piston is reciprocating between the first andsecond positions. When LII the piston moves beyond the second positionand reaches the third position, the annular flange is no longer insealing engagement with the cylinder interior surface whereupon thepiston is restrained by air pressure from returning to the firstposition.

DESCRIPTION For a more complete understanding of the invention referenceshould be made to the drawings wherein:

FIG. l is a side elevational view of a pneumatically operated drivingtool embodying the fail-safe mechanism.

FIG. 2 is an enlarged, fragmentary vertical sectional view of the toolof FIG. l and showing the piston in its firing position with respect tothe cylinder.

FIGS. 3, 4, and S are fragmentary vertical sectional views of thefail-safe mechanism shown in FIG. 2, but with the piston thereof locatedrespectively at the first, second, and third posi tions with respect tothe cylinder.

FIGS. 6, 7, and 8 are similar to FIGS. 3-5, but showing a secondembodiment of the fail-safe mechanism.

FIGS. 9, l0, and 11 are similar to FIGS. 3-5, but showing a thirdembodiment of the fail-safe mechanism assembly.

FIGS. ll2, 13, and 14 are similar to FIGS. 3-5, but showing a fourthembodiment of the fail-safe mechanismi Referring now to the drawings andmore particularly to FIGS. l and 2, a pneumatically operated portablefastenerdriving tool 20 is shown which incorporates one embodiment ofthe fail-safe mechanism 21.

Basically tool 20 comprises a hollow handle section 22, a housing 23disposed at the forward end of the handle section and in which thefail-safe mechanism 2l is disposed, a magazine 24 for fasteners securedto the lower portion of the handle section, and a nose section 25positioned beneath the housing and from which individual fasteners arerapidly expelled.

An air hose connector 27 is provided at the rear of the handle section22 and a trigger control 28 is mounted adjacent the housing 23 formanually controlling the firing of the tool.

In FIG. 2 an enlarged vertical section ofhousing 23 is shown with theimproved mechanism 2l located therein. The housing 23 includes a centralbody portion 23a, a hollow cover portion 23b removably mounted on theupper end thereof, and a bottom portion 23C removably secured to thelower end of portion 23a.

Snugly mounted within body portion 23a is an elongated cylinder 3l), theupper end of which terminates at the cover portion 23b. Resilientlyengaging the upper end of cylinder 30 and disposed within the coverportion is a poppet valve 31. An O-ring type seal 32 is carried by thevalve 3ll and is adapted to sealingly engage the upper edge of thecylinder 30 when the valve is in its closed position. The valve 31 isbiased in the closed position by a coil spring 33. The upper end of thespring contacts the underside of the cover portion 23b and the lower endengages the upper side of the valve 31.

As seen in FIG. 2, valve 31 is provided with a centrally disposedupwardly extending hollow post 34 which is disposed in telescopingrelation within a hollow depending post 35 formed in the hollow coverportion 23b. Posts 34 and 35 are encompassed by the spring 33. Asealing, sliding tit is maintained between the telescoping hollow postsby an O-ring seal 36 which encompasses post 34.

At the upper end of the depending hollow post 35 is affixed an annularseal pad 37 which is engaged by the upper end of post 34, when the valve3l is moved upwardly to its fully open position with respect to theupper end of cylinder 30. When the upper end of post 34 is in contactwith seal pad 37, the central bore 34a formed in post 34 is closed off.

lt will be further noted in FIG. 2 that a peripheral portion 31a ofvalve 3l projects outwardly beyond the exterior of cylinder 3i) andterminates within a cavity 38. The cavity 38 surrounds the upper endportion of the cylinder and communicates with a second cavity 40 chargedwith high pressure air and formed in the handle section 22.

inin'm ,man

Valve 3l carries a second O-ring 41 which encompasses same and is insliding, sealing engagement with the walls forming an annular chamber 42within the interior of cover portion 23h. Chamber 42 communicates withone end ofa passageway 43, the latter having one part thereof formed inthe cover portion 23b and the remaining part formed in the housing 23.The passageway 43 interconnects cavity 40 with chamber 42. Interposedpassageway 43 and cavity 40 is the trigger control 28, which includes ahollow spool 44 disposed in sliding, sealing engagement within a sleeve45, the latter being affixed to the handle section 22. Sleeve 45 isprovided with a transversely extending port 45a which effectscommunication between the lower end 43a of passageway 43 and the centerbore 45h of the sleeve only when the spool 44 is in its normal downposition as seen in FIG. 2. The upper end of the bore 435h is providedwith an inwardly extending collar 45e. Disposed within the bore 45h andintermediate collar 45C and the spool 44 is a coil spring 46 whichserves to bias the spool in its down position` Spool 44 is provided witha center passage 44h, one end of which opens to the atmosphere at thelower exposed end 44a of the spool. The opposite end of passage Mbterminates at a transversely extending port 44C which is spaced from theupper end of the spool. When the spool 44 is manually moved upwardly bya trigger lever 47 which is pivoted in a clockwise direction about pin48, the transversely extending port 44C will register with the lower end43a of passageway 43. The spool 44 carries a pair of O-rings 50a-bdisposed above and below the port 44C which sealingly and slidablyengage sleeve 45 and prevent air leakage between the spool and sleeve.

In normal operation, air pressure is exerted on the upper and lowersurface of poppet valve 31 and due to the fact that the area ofthe uppersurface of the valve 3l exposed to the air pressure is greater than thearea of the under surface of said valve exposed to the same pressure,the valve will remain seated on the upper end of cylinder 30. Coilspring 33 will cause the valve to remain seated when the tool is notconnected to the source of compressed air. The force of spring 33 isovercome by the air pressure exerted on the under surface of valve 3l,when the spool 44 is moved to its up position, because chamber 42 isthen vented to the atmosphere through passageway 43, port 44C, and bore44h.

The upper end of cylinder 30 is provided with an inwardly extendingannular shoulder 30a, the underside of which is slightly chamfered, seeFIG. 2. The function of the shoulder 30a will be discussed more fullyhereinafter.

Mounted for reciprocatory movement within cylinder 30 is a double spooltype piston 51. The upper end of the piston is provided with atransversely disposed annular head 52 the diameter of which is slightlyless than the diameter of the opening delimited by shoulder 30a. Head 52is provided with an annular peripheral groove 52a in which is disposedan O- ring 53. The outer diameter of the O-ring when in an uncompressedstate is greater than the diameter delimited by shoulder 30a. Thus, whenthe piston S2 is in its up or firing position l as shown in FIGS. 2 and3, the O-ring 53 will frictionally engage or become partially wedgedagainst the charnfered surface of shoulder 30a. By reason of thisfrictional engagement, there is a slight delay after the poppet valve 3lhas moved upwardly from the end of cylinder 30 so as to expose the topof the head to the full force of the compressed air be fore the pistonmoves downwardly with respect to the cylinder. Because ofsucli delay, amore effective and powerful driving force is exerted on the piston bythe compressed air. A further advantage resulting from the wedgedrelation which occurs between the periphery of the piston head and thecylinder shoulder 39a, when the piston assumes position I, is that thepiston will not accidentally drop or move towards position ll and thusthe possibility of the fastener feed mechanism becomingjammed isavoided.

Spaced longitudinally beneath head 52 and axially aligned therewith isan annular transversely extending flange 54. The head and flange areinterconnected by a depending stem 55. The diameter of flange 54 is lessthan the diameter of head 52.

A peripheral groove 54a is formed in flange 54 for accommodating anO-ring 56 which is adapted to sealingly and slidably engage the interiorsurface of cylinder 30. lt will bc noted that the lower portion of thecylinder interior is of a reduced diameter.

Adjacent the location where the diameter of the cylinder interior isreduced are provided a plurality of small ports 57 which aresymmetrically arranged in a cylinder-encircling relation, see FIG. 2.The ports 57 effect communication between the cylinder interior and theportion of cavity 38 which substantially surrounds the exterior of thecylinder. When the piston 5l is in its up or firing position I, theupper surface of flange 54 will be located just beneath the row of ports57. Thus, when cavity 38 is charged with compressed air, a portion ofthe compressed air becomes entrapped within the cylinder interiorbetween head 52 and flange 54. The trapped air serves a dual purposeduring normal operation of the piston 5l, namely (a) it gives addedforce to the driving stroke, and (b) it provides a means for effectingrapid return ofthe piston to its firing position after it has reachedthe end ofits firing stroke Il, see FIG. 4.

To cushion the impacting force of piston 5l when it reaches position Il,a bumper 58 is mounted adjacent to but spaced from the lower end ofcylinder 30. The bumper is normally of ringlike configuration and formedof rubber or some synthetic resilient material. The bumper is seatedwithin a pocket 60 formed at the lower end of the housing 23. The bumperis axially aligned with the axis of the cylinder 30 and is provided witha center opening 58a through which a driver blade or hammer rod 6lextends. The blade 6l is attached to the underside of flange The lowerend of the blade is slidably mounted within a stationary guide 25a whichforms a part of the nose section 25.

The lower end of cylinder 3l) engages a shoulder 62 formed in theinterior wall of cylinder 30. As seen in FIG. 2, the lower end ofthecylinder is spaced above the lower end 23C of the housing so as to forman annular chamber 63 which encompasses the upper projecting part of thebumper 58. The chamber 63 is vented to the atmosphere through ports 64and 65. The latter ports 65 are in registered relation with the opening58a formed in the bumper.

When the bumper 58 is operating properly, it will effect cushioning ofthe piston 5l at the end of its firing stroke so that the O-ring 56carried by the flange 54 will remain in sealing engagement with theinterior surface of cylinder 30 thereby preventing the compressed airentrapped between the piston head S2 and flange 54 from escaping intochamber 63 and then out through ports 64 to the atmosphere. If thebumper begins to cavitate or wear due to heat generated by repeatedimpact from the piston, it will no longer cushion the piston 5l when itreaches position ll, but instead will permit the piston to reach anabnormal position lll, see FIG. 5. When the piston has reached positionIll, the O-ring 56 carried by flange 54 will no longer remain insealing, sliding engagement with the interior of cylinder 30 but willmove beyond the lower end limit of the cylinder into the annular chamber63. Once the O-ring S6 is disposed in chamber 63, the entrapped air isvented into the chamber and out through ports 64 and the O- ring resumesan expanded or noncompressed state. When the trapped air has beenreleased, the piston will remain in position III due to the compressedair passing through ports 5'/ and reacting only upon the upper surfaceof head 52, see FIG. 5. Thus, as soon as the piston reaches position IIIthe tool is immediately rendered inoperative whereby no damage to thepiston, cylinder, or the housing is incurred. When the tool is renderedinoperative and the piston remains in its down position, the operatorcan readily ascertain without disassembly of the tool that the bumperhas cavitated and requires replacement.

FIGS. 6-3 show a first modified tool l2@ wherein the bumper i153therefor is provided with a plurality of radially extending grooves lSbformed in the upper surface thereof which effect communication betweenthe chamber l63 and 101029 (mild the center opening llSfla of thebumper. Thus, with tool 120 upon the piston 151 thereof reachingposition III, the compressed air entrapped between the piston head 152and flange 154 will be vented to the atmosphere through chamber 163,grooves 158b, and opening 15811. Notwithstanding the cavitation or wearof bumper 158, the grooves formed in the upper surface thereof are ofsufficient depth to provide the necessary venting communication betweenthe chamber 163 and bumper opening 15841. Aside from this difference,the structure of tools and 120 may be the same.

FIGS. 9-11 show a second modified tool 220 which is substantially thesame as tool 120 except that a bumper 258 is provided in which the uppersurface thereof is substantially dome-shaped and also is provided withone or more radially extending grooves 258b. In tool 220, the housing223 in which the piston and bumper are located is slightly differentfrom that of tool 120; however, in both tools the fail-safe featureembodied therein is basically the same.

The modified tool 320 shown in FIGS. 12-14 differs primarily from thepreviously described tools in that no ports are formed in the cylinderwall through which compressed air enters the cylinder interior andbecomes entrapped between the head 352 and flange 354 of the piston3511. In lieu of the cylinder wall ports, the piston stem 355 is hollowand opens at the upper surface of head 352. A transversely extendingport 35511 is provided which effects communication between the centerbore 355b of the stem and the spacing between the head and flange. A oneway valve 355C is carried by the stem and cooperates with port 355a topermit air to only flow into the spacing through port 355:1.

During normal operation of the piston 351, between positions I and II,high pressure air flows through bore 355b and port 355a into and becomestrapped within the spacing between the head and flange of the piston. Itis the entrapped compressed air which facilitates return of the pistonto its initial or firing position l. As in the case of tool 2f), tool320 is provided with a chamber 363 into which the entrapped cornpressedair is vented when the piston 351 assumes position III due to cavitationof the bumper 358. A port 3641 is provided in housing 323 which in turnvents chamber 363 to the atmosphere.

As will be observed, the operation of the fail-safe mechanism in each ofthe tools 20, 120, 220, and 320 is substantially the same and providesthe necessary protection for the various component parts of the toolwhile at the same time giving the operator of the tool immediate noticewhen an abnormal operating condition exists. With the fail-safemechanism heretofore described, the existence of a defective bumper canbe readily determined without requiring disassembly of the tool. Thefail-safe mechanism reduces the downtime of the tool because replacementof the bumper is required only when cavitation of the bumper hasactually occurred.

Iclaim:

1l. A fail-safe mechanism for a pneumatic fastener-driving toolcomprising an elongated cylinder; a double spool type piston mountedwithin said cylinder for reciprocatory movement between first and secondlongitudinally spaced positions and immovable when disposed at a thirdposition adjacent said second position but spaced a greater longitudinaldistance from said first position, said piston including a head havingthe periphery thereof in sliding, sealing engagement with the cylinderinterior surface, and a flange longitudinally spaced from said head andmovable therewith as a unit, said flange having the periphery thereof insliding, sealing engagement with the cylinder interior surface only whensaid piston is disposed at or between said first and second positions,and being out of sealing engagement with said interior surface only whensaid piston is disposed at said third position, said head having agreater air pressure-responsive surface area than said flange; means forexerting a predetermined air pressure on said head to effect movement ofsaid piston from said first position towards said second or thirdpositions; means whereby air is entrapped between sald head and saidflange and the pressure of said entrapped air becomes greater than saidpredetermined air pressure only when said piston is disposed at saidsecond position and during predetermined segments of travel from saidsecond to said first positions; means for automatically releasing theentrapped compressed air from between said head and flange only whensaid piston is disposed at said third position; and resilientpiston-engaging stop means for normally cushioning and retarding themovement of said piston when the latter has reached said secondposition.

2. The mechanism of claim 1 including manual control means forregulating the application of said predetermined air pressure on saidpiston head.

3. The mechanism of claim ll wherein said stop means is removablymounted adjacent one end of said cylinder.

4. The mechanism of claim 1l wherein said cylinder includes a first airinlet adjacent said first position and a second air inlet disposedintermediate said first and second positions; the longitudinal distancebetween said second air inlet and the location of said flange, when saidpiston is in either said second or third positions, being greater thanthe longitudinal distance between said flange and head.

5. The mechanism of claim l wherein said piston includes driverblade-attaching means disposed on the end thereof` opposite said head.

6. The mechanism of claim 5 wherein said stop means is of ringlikeconfiguration, and said driver blade-attaching means is axially alignedwith respect to the center of said stop means,

7. The mechanism of claim 2 including a housing for said cylinder, saidhousing being provided with a handle on which said manual control meansis mounted.

8. The mechanism of claim 5 including a housing for accommodating saidcylinder, said housing being provided with conduit means communicatingwith said first and second air inlets.

9. The mechanism of claim when said housing is provided with an annularchamber disposed endwise of said cylinder and adjacent said thirdposition, said piston flange being located within said chamber only whensaid piston is disposed at said third position whereby the compressedair entrapped between the head and flange of said piston is vented tosaid annular chamber; said housing being provided with means for ventingsaid chamber to the atmosphere.

1. A fail-safe mechanism for a pneumatic fastener-driving toolcomprising an elongated cylinder; a double spool type piston mountedwithin said cylinder for reciprocatory movement between first and secondlongitudinally spaced positions and immovable when disposed at a thirdposition adjacent said second position but spaced a greater longitudinaldistance from said first position, said piston including a head havingthe periphery thereof in sliding, sealing engagement with the cylinderinterior surface, and a flange longitudinally spaced from said head andmovable therewith as a unit, said flange having the periphery thereof insliding, sealing engagement with the cylinder interior surface only whensaid piston is disposed at or between said first and second positions,and being out of sealing engagement with said interior surface only whensaid piston is disposed at said third position, said head having agreater air pressureresponsive surface area than said flange; means forexerting a predetermined air pressure on said head to effect movement ofsaid piston from said first position towards said second or thirdpositions; means whereby air is entrapped between said head and saidflange and the pressure of said entrapped air becomes greater than saidpredetermined air pressure only when said piston is disposed at saidsecond position and during predetermined segments of travel from saidsecond to said first positions; means for automatically releasing theentrapped compressed air from between said head and flange only whensaid piston is disposed at said third position; and resilientpistonengaging stop means for normally cushioning and retarding themovement of said piston when the latter has reached said secondposition.
 2. The mechanism of claim 1 including manual control means forregulating the application of said predetermined air pressure on saidpiston head.
 3. The mechanism of claim 1 wherein said stop means isremovably mounted adjacent one end of said cylinder.
 4. The mechanism ofclaim 1 wherein said cylinder includes a first air inlet adjacent saidfirst position and a second air inlet disposed intermediate said firstand second positions; the longitudinal distance between said second airinlet and the location of said flange, when said piston is in eithersaid second or third positions, being greater than the longitudinaldistance between said flange and head.
 5. The mechanism of claim 1wherein said piston includes driver blade-attaching means disposed onthe end thereof opposite said head.
 6. The mechanism of claim 5 whereinsaid stop means is of ringlike configuration, and said driverblade-attaching means is axially aligned with respect to the center ofsaid stop means.
 7. The mechanism of claim 2 including a housing forsaid cylinder, said houSing being provided with a handle on which saidmanual control means is mounted.
 8. The mechanism of claim 5 including ahousing for accommodating said cylinder, said housing being providedwith conduit means communicating with said first and second air inlets.9. The mechanism of claim 8 when said housing is provided with anannular chamber disposed endwise of said cylinder and adjacent saidthird position, said piston flange being located within said chamberonly when said piston is disposed at said third position whereby thecompressed air entrapped between the head and flange of said piston isvented to said annular chamber; said housing being provided with meansfor venting said chamber to the atmosphere.